1. Field of the Invention
The present invention relates to a circuit module incorporating electronic parts, and a process for producing the same, and more specifically, it relates to a circuit module that is prevented from suffering invasion of foreign matters into a cavity, and a process for producing the same.
2. Description of Related Art
A high-frequency circuit module used for communication equipments, artificial satellites, radar equipments and the like necessarily has high reliability and prolonged service life. Accordingly, circuit regions thereof having high-frequency electronic parts mounted therein are hermetically sealed with a cap having a cavity.
The cap of the high-frequency circuit module is formed of a metal or a dielectric material having an electroconductive surface for blocking leakage of electromagnetic waves from the high-frequency electronic parts and for shielding the high-frequency electronic parts from interference of external electromagnetic waves. It is necessary to prevent the circuit regions of the high-frequency circuit module from suffering interference of electromagnetic waves among the respective circuit regions. Accordingly, the cavity is divided into plural cells by barriers, and the circuit regions are housed in the divided cells, respectively.
For example, such a high-frequency circuit module has been known that has high-frequency circuit regions hermetically sealed with a metallic flat container main body having pin terminals hermetically sealed, and a metallic cap (which is hereinafter referred to as a lid) having plural cavities formed with partitions (as described, for example, in JP-B-07-073123 (page 2 and FIG. 1)).
In the high-frequency circuit module, the terminals for retrieving signals are hermetically sealed since the flat container main body is formed of a metal. In recent years, however, a dielectric material substrate, instead of a metal, is used as the flat container main body for simplifying the production process of the container main body and for reduction of the cost thereof.
For example, such a hermetically sealed semiconductor device has been known in that a ceramic substrate having a circuit pattern for mounting electronic parts is used as the flat container main body of a dielectric material substrate (as described, for example, in JP-A-2001-68576 (page 3 and FIG. 1)).
A dielectric material substrate, such as a ceramic substrate, used as the flat container main body cannot be joined to the lid by welding, which has been used for joining a metallic container main body, and therefore, the flat container main body is joined to the lid with solder or adhesive.
In the case where the ceramic substrate as the flat container main body is joined to the lid with solder, however, a solder paste is used, and voids due to remaining flux contained in the solder paste burst upon heating for joining, whereby solder balls are scattered within the space inside the cavity having the electronic parts housed therein. The flux remaining in the solder layer is also scattered within the space inside the cavity having the electronic parts housed therein. The solder balls and the flux scattered within the space inside the cavity bring about a problem on operation and characteristics of the electronic parts sealed in the cavity.
In the case where the ceramic substrate as the flat container main body is joined to the lid with adhesive, an electroconductive resin is used for joining. In this case, voids formed in the electroconductive resin due to coating of the electroconductive resin burst upon joining the flat container main body and the lid, and particles of the electroconductive resin are scattered within the space inside the cavity having the electronic parts housed therein and bring about a problem on operation and characteristics of the electronic parts sealed in the cavity.